Wrinkles fade out when retopologizing
The big wrinkles should be sculpted and the small ones should be painted after the retopology and after baking the normals.
If your model is meant to be rendered within Blender, you can restore lost detail on the retopologized model by adding a multiresolution modifier and a shrinkwrap modifier that you apply (only the shrinkwrap). Note that you have to apply it while the shrinkwrap is below the multires, otherwise it doesn't work.

Painting on a triangle mesh is a bad idea.